The embodiments described herein relate generally to a rotor for use in an electric machine, and more specifically, to an apparatus and method associated with a rotor for use in an axial flux electric motor.
A common configuration for an electric motor is radial-flux, which is composed from two cylinders, a cylindrical stator and a cylindrical rotor (having an axial shaft), with a cylindrical air gap in between and in which the flux travels across the air gap in a direction that is radial to the shaft on the rotor. In order to hold the two cylinders concentric and thus keep the air gap constant thickness in a radial flux motor, it is necessary to support the shaft at each end of the motor.
Given that many applications which are mechanically powered by a radial-flux electric motor do not intrinsically require a shaft, it is desirable to eliminate the necessity for a shaft and thus provide a cheaper and simpler structure. An axial flux motor is one such structure.
Further, many applications which are mechanically powered by a radial-flux electric motor provide for ample landscape for a large diameter motor but little room along the longitudinal axis of the shaft. An axial flux motor is well suited to such applications as the axial flux motor with high motor power capacity may indeed have a very short axial shaft length.
Typically an axial flux motor includes a rotor having one or more permanent magnets mounted to a face of the rotor and a stator having a stator winding connected to a power source. The motor also includes a bearing positioned between the rotor and the stator for rotationally supporting movement of the rotor relative to the stator. The bearing provides an air gap between the rotor and the stator. The permanent magnets can be replaced by a magnet field induced by an electrical winding.
Due to its high speed operation, it is desirable to provide a rotor with a low mass. To provide a motor with sufficient power in operation, it is desirable to provide a rotor with a large diameter rotor. Providing a motor with a rotor that has both a large diameter and a low mass, yet able to be sufficiently rigid for high speed operation provides a challenge. Further, providing such a rotor at low cost is increasingly difficult.
The efficiency of motors may be improved by providing the magnetic flux of the rotor with permanent magnets attached to the rotor. Such magnets are typically called permanent magnet motors and are typically more efficient than motors that do not use permanent magnets, typically induction motors. One type of permanent magnet motor utilizes electronics to time the energizing of the stator coils and is called an electronically commutated motor or ECM motor.
Such permanent magnet and ECM motors may use stronger magnets to further improve their efficiency. One type of such stronger magnet are called rare earth magnets and are made of rare earth metals, for example, neodymium. Neodymium magnets have been very expensive and their cost has been very volatile, particularly in recent years.
The present invention is directed to alleviate at least some of these problems with the prior art.